Welding robots are known which are designed to assemble parts, for example to weld electronic components onto a printed circuit. In the known devices, the welding operation is carried out using a mobile bit brought into contact with the part to be welded and a metal wire having a low fusion point maneuvered in such a manner that its extremity touches the parts to be welded when these are heated by the bit. Devices of this kind are easy, to manipulate since the temperature of the bit is low enough to ensure that the radiation which it generates does not affect the environment of the parts to be welded or the areas swept during passage from one working point to another. The quality of the weld obtained using a device of this type is unfortunately inferior to that achieved using a flame gas welding torch. This is due to the fact that the welding torch makes it possible to attain temperatures higher than those obtained using a bit and hence to obtain a more liquid weld, ensuring a better quality join.
Welding heads are also known which are designed to be mounted on a robot and equipped with a welding torch making it possible to use flame gas welding Nevertheless devices of this type have a disadvantage which complicates their use. The temperature of the burning gas is very high and can reach 2700.degree. C. The robot program thus has to provide for displacement of the head so that the flame cannot destroy or ignite any of the parts located on the working table. The flame consequently has to be moved back a considerable distance from the working surface when it is moved from one work station to another. As a result, the time taken to complete one operation is significantly lengthened.
One possibility would be to lower the flame or even extinguish it before moving the head. However, some fifteen seconds unfortunately elapse before the flame is stabilized after being lit, or after any substantial change in its intensity This, too, also lengthens the working time.